Steel shim head Gasket

1971-valiant-RT said

Wierd there was one on my 1975 pickup when I took the motor apart. I still have it.

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The factory installed gasket was the "shim" gasket. These gaskets have been NS1 for a few years, now. All the aftermarket head gaskets are the thicker type. When using an aftermarket gasket, you will lose a little compression. When replaceing a slant six head gasket, with an aftermarket gasket, it is desireable to mill the head, 10 to 20 thousands to put the compression back to factory.
If you do mill the head, you might as well mill some extra, to increase the compression, as the factory ratio numbers were optomistic (most slants will measure at less then 8 to 1), and the added compression, will add power, and increase fuel economy.